The present invention relates to an apparatus for supplying power for a vehicle, which is able to implement redundancy, and more particularly relates to an apparatus for supplying power for a vehicle which is applied to by-wire systems, such as a steer-by-wire system, a brake-by-wire system and the like.
As for a power supply system for a vehicle which implements redundancy, Japanese Published Patent Application 2003-226207 discloses related arts. In this document, plural batteries are electrically connected in parallel to the load devices of a vehicle so as to establish redundancy. When the remaining capacity of a main battery falls below a predetermined threshold, switching from the main battery to a sub battery is executed.
As for a technique to improve the reliability of a by-wire system, Japanese Published Patent Application 2001-171543 discloses related arts. This document discloses a steer-by-wire system which has a mechanical failsafe device. In the event that such a trouble as loosening of a power terminal or deterioration of a battery makes it impossible to supply power to the system, a steering mechanism is made ready by a clutch provided between a wheel shaft and a rack shaft. In this way, even if the steer-by-wire system does not work, it is possible to avoid a catastrophic trouble such as losing of steering.
Although the technique disclosed in Japanese Published Patent Application 2003-226207 which makes provision for automatic switching from the main battery to the sub-battery in the event of deterioration of the main battery, there is no guaranteeing that the sub-battery can always be kept in sound conditions. For example, when the remaining capacity of the main battery falls due to self discharge, the load devices are automatically connected to the sub-battery by switching. Therefore, it is not always possible to guarantee that the sub-battery always supplies stable power to the load devices after switching.
Because a highly reliable power supply is required for a system such as a steer-by-wire (SBW) system or a brake-by-wire (BBW) system, it is mandatory that stable supply of power to the system should be always implemented both before and after switching from the main battery to the sub-battery, which serves as a backup. In this regard, the apparatus disclosed in Japanese Published Patent Application 2003-226207 is not satisfactory.
The technique disclosed in Japanese Published Patent Application 2001-171543 introduces a wheel shaft aiming at failsafe mechanism in order to mitigate a concern over the reliability of a power supply during supply of power to the steer-by-wire system. However, the technique adversely requires a complicated arrangement, leaving an intrinsic problem associated with the reliability of power supply unsolved.
Similarly, a brake-by-wire system driven by a motor has been developed, which serves as an alternative for hydraulic control with pipes of working-fluid. This system does not solve the same problem associated with the reliability of power supply, either.